Dental caries remains among the most prevalent infectious diseases worldwide. Over 84 percent of U.S. children, 96 percent of U.S. adults, and 99.5 percent of Americans 65 years of age and older have experienced tooth decay. Overall, caries appears not to be under control, even in industrialized countries. The best control strategies for caries involve reducing the virulence of the pathogens. Streptococcus mutans is recognized as the principal etiological agent of dental caries. The ability to metabolize carbohydrates and to adhere to and form tenacious biofilms on the tooth surfaces are believed to be critically associated with the cariogenicity of this human pathogen. Although numerous studies have elucidated the mechanisms of initial attachment, not all the factors that are involved in biofilm formation have been identified. Moreover, very little is known about the regulation of expression of these factors on the S. mutans cell-surfaces. Therefore, we have chosen to identify and study the expression of these cell surface proteins. We found that a functional HtrA (a serine protease needed for processing and maturation of proteins) is required for biofilm formation in S. mutans. Since we also found that HtrA modulates expression of various cell-surface proteins, we hypothesize that some of those HtrA regulated cell-surface proteins are required for biofilms. In this proposal, in Specific Aim 1, we will identify those cell-surface proteins that need functional HtrA. HtrA acts as both protease and chaperone. Because chaperone activity is needed for proper protein folding, we propose that chaperone activity is also involved in cell-surface expression of proteins. In specific Aim 2, we will test this hypothesis using two cell-surface proteins, enolase and glyceraldehydes-3-phosphate dehydrogenease, that were affected by an htrA null mutation: A clearer understanding of the regulation of extracellular/cell-surface protein expression in S. mutans will provide opportunities for the development of new approaches to the prevention and treatment of dental caries. [unreadable] [unreadable] [unreadable]